In recent years, robot arms are being used cooperatively with people among production facilities, and also used for assistive aids in daily life to maintain or improve the quality of life of elderly people and people with disabilities.
One typical example of the robot arms is a robot arm having an arrangement as illustrated in (a) and (b) of FIG. 27. That is, the robot arm includes a base portion 100, an end effector 101, and arm sections 102 serially connected via rotational joints 103 between the base portion 100 and the end effector 101. However, in this arrangement, the arm sections 102 largely project laterally from a line (a dotted line in the figure) that connects the base portion 100 and the end effector 101, when the robot arm is folded as illustrated in (b) of FIG. 27. This increases such a risk that a projected portion strikes or hits an object around the robot arm. Further, there is a risk that an object around the robot arm may be caught between the arm sections 102. In view of this, it can be said that this robot arm is not suitable especially as an assistive robot arm used in daily life.
One exemplary structure of a robot arm that can reduce these risks may be a thin-stick-like structure in which an end effector and a base portion are linearly connected via a stick-like member. (a) to (d) of FIG. 28 illustrate 4 types of telescopic robot arms having a “linear-motion telescopic mechanism” in which the stick-like member performs linear telescopic motion, whereby an arm function works out. (a) of FIG. 28 is a view illustrating an ideal thin telescopic arm in which any mechanism having a telescopic function is provided. (b) to (d) of FIG. 28 illustrate telescopic arms that symbolize some concrete mechanisms. In these arrangements, a space to be occupied by arm sections is minimized as compared with that of the arrangement in FIG. 27, which advantageously minimizes a degree of obstruction in user's view. However, in these three types of arrangements of (b) to (d) of FIG. 28, in order to achieve sufficient stiffness, it is necessary to design the real mechanisms thick in a contraction state, thereby resulting in that the appearances of these mechanisms look quite unlike the appearance of the ideal arm section illustrated in (a) of FIG. 28. In other words, the mechanisms of (b) to (c) of FIG. 28 must be of an undesirably large shape. A general reason why these mechanisms should be made so thick is as follows: sufficient stiffness requires sufficient thickness of the arm sections; and a sufficient moving space of the end effector requires a sufficient difference in arm length between an elongate state and a contraction state. As a result, a volume, i.e., a product of the thickness and the length, of an arm structure for an unnecessary portion in the contraction state (hereinafter referred to as an unnecessary portion of the arm section) gets quite bulky, and a volume necessary to house the unnecessary portion makes the base portion and its auxiliary mechanism larger.
Besides the robot arms exemplified above, there have been reported many robot arms having a linear-motion telescopic mechanism (see Patent Literatures 1, 2, 3). However, these robot arms are not produced from the viewpoint of avoiding the aforementioned risk of getting caught between arm sections or for the purpose of being used beside people. In view of this, it is difficult to use these robot arms beside people in daily life or among production facilities, which would be a problem to be solved in the present invention.
Further, a two-legged robot having a linear-motion link mechanism has been reported (see Patent Literature 4). However, the two-legged robot is a very ambitious device, and therefore unsuitable for a robot arm, which requires weight saving.